Fog storage's #clean_cache! breaks when non-cache objects exist in cache_dir

Closes #2532

Author: mshibuya

lib/carrierwave/storage/fog.rb

@@ -147,8 +147,9 @@ def clean_cache!(seconds)
           :public => uploader.fog_public
         ).files.all(:prefix => uploader.cache_dir).each do |file|
           # generate_cache_id returns key formated TIMEINT-PID(-COUNTER)-RND
-          time = file.key.scan(/(\d+)-\d+-\d+(?:-\d+)?/).first.map { |t| t.to_i }
-          time = Time.at(*time)
+          matched = file.key.match(/(\d+)-\d+-\d+(?:-\d+)?/)
+          next unless matched
+          time = Time.at(matched[1].to_i)
           file.destroy if time < (Time.now.utc - seconds)
         end
       end

spec/storage/fog_helper.rb

@@ -338,6 +338,19 @@ def check_file
         end
         expect(@directory.files.all(:prefix => 'uploads/tmp').size).to eq(0)
       end
+
+      context "when a file which does not conform to the cache_id format exists" do
+        before do
+          @directory.files.create(:key => "uploads/tmp/invalid", :body => 'A test, 1234', :public => true)
+        end
+
+        it "should just ignore that" do
+          Timecop.freeze(today) do
+            @uploader.clean_cached_files!(0)
+          end
+          expect(@directory.files.all(:prefix => 'uploads/tmp').size).to eq(1)
+        end
+      end
     end
 
     describe "CarrierWave::Storage::Fog::File" do